1. Field of the Invention
This disclosure relates to the field of filtration for environmental control units (ECUs). Particularly to filtration units for providing an isolated environment from Nuclear, Biological, or Chemical (NBC) contamination for use with portable ECUs which preserve filter life when NBC filtration is not needed.
2. Description of the Related Art
In recent years the need to segregate individuals from dangerous substances in the air has become one of increasing interest. All human beings must breath and the introduction of airborne agents to the air they inhale creates a dangerous situation whereby individuals can be killed or injured and can strain medical response capability in an area. While all environmental air contains some impurities which can harm those breathing it, such as cold viruses and pollutant molecules, modern warfare, terrorism, technology changes, and increasing globalization have led to an increased likelihood of larger scale contamination of air wherein sources of clean air can become quickly necessary to prevent catastrophic outcomes.
The danger of a chemical, biological or nuclear weapon being unleashed on military forces, or on civilian centers, is a nightmare scenario for many government organizations. Such an attack can stimy military effectiveness, or bring day to day economic activity to a grinding halt. Even without the purposeful use of nuclear, biological, or chemical weapons, the possibility of accidents involving these agents in populated areas is also a danger and governments must be able to respond to protect the citizenry. Still further, increases in globalization have led to increased danger of communicable disease. The recent Severe Acute Respiratory Syndrome (SARS) outbreak and fear of other dangerous natural contagions transmitted in the air has dramatically highlighted the need for governments and emergency response agencies to be able to quickly provide safe working conditions for health workers and other emergency responders to deal with contaminants, whether natural or man-made, whenever and wherever may be necessary.
The need to provide safe air supplies is one which tends to come upon a population suddenly. The need may be predicted, or an increased risk may be known to be likely such as when military operations are occurring against a government known to possess nuclear, biological, or chemical arsenals, but generally the threat is only realized once the contaminant is present.
Generally, protection against contamination requires the ability to either provide air which is known to be safe and has been stored for use during the period of contamination, or to filter air which is contaminated to remove the contamination and provide safe air. The use of stored air is generally less effective as the storage requires specialized tanks and processes, and generally the amount of air which can be stored is relatively small. Instead, filtration is generally used, particularly if one is attempting to provide safe air to a group of individuals.
Filtration for harmful contaminants generally works by filtering out any of three classifications of contaminants. These are nuclear, biological, or chemical (NBC) threats. NBC filters serve to reduce concentrations of nuclear particulates, organisms, and chemicals to levels where their concentration is no longer harmful, or in the worst case, no longer debilitating.
Larger isolation structures which can house multiple individuals are often the preferred method of providing safe air to groups of individuals. Isolation structures can have economies of scale for NBC filtration where larger more powerful air intake devices can be used to supply air to the structure. Further, a structure can allow individuals therein to perform tasks as they normally would instead of being forced to work in cumbersome individual protective suits.
Isolation structures may be permanent or may be temporary. In emergency responses or military field activities, a temporary structure is generally preferred as it can be quickly setup anywhere when needed, and more easily stored when not needed. Often the temporary structure is inflatable whereby the structure can be setup in the zone of contamination and can then be filled with clean air using a portable filtration system, the air providing the shape to the structure. Once inflated, the structure will be able to provide a safe haven for multiple people and a staging point for the use of contamination suits to venture further into a contaminated area. Further, the structure can be provided with more effective heating, cooling, or other environmental modification.
For many of these temporary structures, the environment inside the structure is maintained using an environmental control unit (ECU) (50) such as that shown in FIG. 1A. The ECU (50) is generally portable (generally being vehicle or pallet mounted) and serves to provide air to the inside of the structure. In order to provide safe air into the structure, the ECU (50) generally needs to be able to pump in dirty air and filter it or be provided with safe air at intake (5), and then pump the air into the structure. Traditionally, on a portable ECU (50), the filter (3) was a separable component which could be placed in the incoming air path of the ECU (50) to filter the air if necessary. In this way, the isolation structure (10) could be set up and used in a safe area without need to install the filter (3) on the intake if filtered air was not required. If the threat of NBC contamination was present, the same air intake could be modified to include a filter and provide filtered air. Both such options are shown in FIG. 1B.
This design, however, has a major limitation. If the system is used where there is an ever present threat of contamination, but the contamination is either not constant, or is unknown, the filter (3) must be placed in the air path at all times in order to be safe. Because of current limitations, it has proven difficult to measure the effective life of a filter (3) in operation without knowledge of the environment that the filter (3) is filtering. Further, changing the filter (3) generally requires a potentially hazardous operation, and the filter setup is also much more complicated, as shown in FIG. 1B, than the non-filter setup. In the filter setup, multiple additional hoses (1) and the filter (3) and blower units (7) must be attached to the intake (5) using a special adapter (9) to allow for shelter air to be recirculated with make-up air brought in from the filters (3).
Because of the necessity to operate the ECU (50) with the filter (3) in place during a threat, even if the actual danger is not continuous or does not materialize, the operation of the structure (10) uses up filters (3) at an increased and unnecessary rate. As a filter (3) is always in use, the remaining useful life of the filter (3) is not actually known. The amount of threat filtered, and the amount of other filter (3) degradation, cannot be accurately determined. Therefore a “safe” estimate is used whereby the filter (3) is replaced based on its time in operation regardless of what it actually filtered. This leads to unnecessary work, the disposal of filters (3) which still have operational life, and an increased cost to both build and transport filters (3). Still further, as a filter (3) necessarily creates air resistance, and a system operating with an unnecessary filter (3) in place wastes energy to pull in air. An additional problem is that if the system is setup in anticipation of a potential danger which does not materialize, the filter (3) may have to be disposed of after a use due to filtering out other containments which are not particularly dangerous or because of lack of knowledge of the load on the filter (3) during its operational time. This can lead to the filter changing operation having to occur during the time when the filter (3) is actually needed.
NBC filters for ECU filtration are part of the significant logistic trail in both military and civilian collective protection and can also be a significant expense. To date, there is no production system that incorporates a method to measure the absorbent level of the carbon bed used in most filters. In the absence of this, protocol dictates that the filter (3) be changed more frequently than needed when it is in use. Each change of filter (3) requires personnel to leave their protected environment and to manually change the filter (3). As well as being a tedious task, it offers the possibility that the filter (3) might not seat correctly, leaving the system potentially at risk and the danger that personnel may be exposed while outside the shelter.
One proposal to attempt to deal with the need to change filters (3) are regenerative filtration systems whereby the filter can be remotely cleaned. There are numerous different types of these proposed such as pressure swing, temperature swing, electronic swing and hybrid systems thereof. Regenerative filtration systems, while effective, are bulky and consume more power and, hence, are only useable in certain applications. In other structures, particularly those where the ECU must be easily portable and the shelter is temporary, or those where the cost of a regenerative filter based on its time of expected use (e.g. such as for civilian emergency preparedness for threats such as a biological terrorist attack) leads to them being uneconomical, disposable filters are superior choices.